1. Field of the Invention
This invention generally relates to digital wrapper format communications and, more particularly, to a system and method for transporting fault type and fault location (FTFL) messages between simplex devices in a network using a digital wrapper format.
2. Description of the Related Art
Digitally wrapped, or multidimensional frame structure communications generally describe information that is sent as a packet without overhead to control the communication process. The packet can also include forward error correction (FEC) to recover the payload if the communication is degraded. One example of such a communication is the synchronous optical network (SONET). Another example is the digital wrapper format often used in transporting SONET communications.
There are many framed communication protocols in use, depending on the service provider and the equipment being used. These differences in protocols can be arbitrary or supported by an underlying function. Frame synchronization and overhead placement are sometimes standardized by governing organizations such as the ITU-T. At the time of this writing, the ITU-T standard for the digital wrapper format is G.709.
Conventionally, the interface node must include two sets of equipment. A communication in the first protocol is received at the first set of equipment (processor). The message is unwrapped and the payload recovered. Synchronization protocols must be established between the equipment set and a second set of equipment (processor). The payload can then be received at the second equipment set and repackaged for transmission in a different protocol.
The G.709 FTFL message is a 256 byte structure that consists of 1 byte per frame for 256 consecutive frames. The 256-byte structure is divided into a 128-byte forward message and a 128-byte backward message. Upon detection of certain error conditions, the receiving device must generate a 128-byte message to be sent upstream. The receiving node examines the overhead field and all the received data bits in payload portion of the G.709 frame to determine if this error condition exists. Once the receiving node has determined that the error exists, it must then generate the 128-byte message and inject it into the data stream in the backward direction.
FIG. 1 is a schematic block diagram of a full-duplex processing node (prior art). When a G.709 compliant full-duplex processing node is built up from a single integrated circuit device, all the communication of the FTFL in the backward direction takes place within that integrated circuit. However, G.709 compliant full-duplex processing nodes can also be built up from two simplex devices, in which case it is no longer possible to communicate the backwards FTFL information within a single integrated circuit. For G.709 compliant systems built with two simplex integrated circuit devices, it is extremely difficult to transfer the FTFL information from the forward to the backward direction. Devices designed to receive a G.709 data stream do not normally need to access the received backward fields because they are used for performance monitoring statistics by the receiving integrated circuit, and are then discarded.
It would be advantageous if two simplex processors could be easily integrated to communication backward messages in a G.709 network.
It would be advantageous if two simplex devices could be integrated in such a way as to communicate the backwards messages in real-time.
It would be advantageous if two simplex devices could be integrated to communicate G.709 FTFL backward messages without complicated interfacing circuitry.